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EPHB4

Official Full Name
EPH receptor B4
Organism
Homo sapiens
GeneID
2050
Background
Ephrin receptors and their ligands, the ephrins, mediate numerous developmental processes, particularly in the nervous system. Based on their structures and sequence relationships, ephrins are divided into the ephrin-A (EFNA) class, which are anchored to the membrane by a glycosylphosphatidylinositol linkage, and the ephrin-B (EFNB) class, which are transmembrane proteins. The Eph family of receptors are divided into 2 groups based on the similarity of their extracellular domain sequences and their affinities for binding ephrin-A and ephrin-B ligands. Ephrin receptors make up the largest subgroup of the receptor tyrosine kinase (RTK) family. The protein encoded by this gene binds to ephrin-B2 and plays an essential role in vascular development. [provided by RefSeq, Jul 2008]
Synonyms
HTK; MYK1; HFASD; CMAVM2; LMPHM7; TYRO11;
Bio Chemical Class
Kinase
Protein Sequence
MELRVLLCWASLAAALEETLLNTKLETADLKWVTFPQVDGQWEELSGLDEEQHSVRTYEVCDVQRAPGQAHWLRTGWVPRRGAVHVYATLRFTMLECLSLPRAGRSCKETFTVFYYESDADTATALTPAWMENPYIKVDTVAAEHLTRKRPGAEATGKVNVKTLRLGPLSKAGFYLAFQDQGACMALLSLHLFYKKCAQLTVNLTRFPETVPRELVVPVAGSCVVDAVPAPGPSPSLYCREDGQWAEQPVTGCSCAPGFEAAEGNTKCRACAQGTFKPLSGEGSCQPCPANSHSNTIGSAVCQCRVGYFRARTDPRGAPCTTPPSAPRSVVSRLNGSSLHLEWSAPLESGGREDLTYALRCRECRPGGSCAPCGGDLTFDPGPRDLVEPWVVVRGLRPDFTYTFEVTALNGVSSLATGPVPFEPVNVTTDREVPPAVSDIRVTRSSPSSLSLAWAVPRAPSGAVLDYEVKYHEKGAEGPSSVRFLKTSENRAELRGLKRGASYLVQVRARSEAGYGPFGQEHHSQTQLDESEGWREQLALIAGTAVVGVVLVLVVIVVAVLCLRKQSNGREAEYSDKHGQYLIGHGTKVYIDPFTYEDPNEAVREFAKEIDVSYVKIEEVIGAGEFGEVCRGRLKAPGKKESCVAIKTLKGGYTERQRREFLSEASIMGQFEHPNIIRLEGVVTNSMPVMILTEFMENGALDSFLRLNDGQFTVIQLVGMLRGIASGMRYLAEMSYVHRDLAARNILVNSNLVCKVSDFGLSRFLEENSSDPTYTSSLGGKIPIRWTAPEAIAFRKFTSASDAWSYGIVMWEVMSFGERPYWDMSNQDVINAIEQDYRLPPPPDCPTSLHQLMLDCWQKDRNARPRFPQVVSALDKMIRNPASLKIVARENGGASHPLLDQRQPHYSAFGSVGEWLRAIKMGRYEESFAAAGFGSFELVSQISAEDLLRIGVTLAGHQKKILASVQHMKSQAKPGTPGGTGGPAPQY
Open
Disease
Brain cancer, Cystic/dysplastic kidney disease, Lung cancer, Metastatic meninges neoplasm, Metastatic tumour, Solid tumour/cancer
Approved Drug
0
Clinical Trial Drug
1 +
Discontinued Drug
0

Detailed Information

Eph receptors, the largest family of receptor tyrosine kinases (RTKs), are involved in critical cell communication processes, especially during embryonic development. Two main subclasses—EphA and EphB—are included. By use of ephrins, membrane-bound ligands, these receptors interact to mediate bidirectional communication controlling cell adhesion, migration, and tissue formation. Linked to many disorders, including cancer, dysregulation of Eph/ephrin signaling is associated with tumor development, metastases, and angiogenesis. Among these receptors, EphB4 has attracted interest for its function in mesothelioma, head and neck cancer, and lung cancer as well as other upper aerodigestive cancers.

EphB4 Receptor Structure and Function

Characteristically a type I transmembrane receptor, EphB4 has a single transmembrane segment, a multidomain extracellular region, and a cytoplasmic kinase domain. Two fibronectin type III repetitions, a cysteine-rich area with an epidermal growth factor (EGF)-like motif, and a globular ligand-binding domain define the extracellular domain. These structural elements let EphB4 bind its ligands—mostly ephrinB2—with great affinity. EphB4 interacts mostly with ephrinB2, a major role in vascular development and tumor angiogenesis, but shows lower binding to ephrinB1 and ephrinB3.

EphB4's cytoplasmic domain features protein interaction modules including a PDZ-binding motif and a sterile-α-motif (SAM) as well as a tyrosine kinase region. At the plasma membrane, these regions help receptor dimerization, oligomerization, and the building of signaling complexes. Together modulating cell adhesion, migration, and segregation, EphB4's signaling pathway consists of both forward signaling (from the receptor-expressing cell) and backward signaling (from the ephrin-expressing cell).

They include two major subclasses: EphA and EphB. These receptors interact with membrane-bound ligands called ephrins, mediating bidirectional signaling that regulates cell adhesion, migration, and tissue development. Dysregulation of Eph/ephrin signaling is linked to various diseases, notably cancer, where it contributes to tumor growth, metastasis, and angiogenesis. Among these receptors, EphB4 has gained attention for its role in upper aerodigestive cancers, including lung cancer, head and neck cancer, and mesothelioma. This article reviews EphB4's structure, its involvement in cancer pathobiology, and the potential for targeting it in therapeutic strategies.

Figure 1 illustrates a working model of Eph receptor function, showing how Eph-ephrin interactions in normal cells lead to tumor suppression, while disruption of these interactions in tumor cells, along with crosstalk with other receptor tyrosine kinases, promotes tumor progression and malignancy.Figure 1. Eph Receptor Function in Tumor Suppression and Promotion. (Salgia R, et al., 2018)

Studies have elucidated the specificities of EphB4-ephrinB2 interactions at the molecular level. Structural studies show that ligand binding depends critically on L95 in EphB4; alterations at this site change binding affinity. These revelations help create therapy plans meant to change EphB4 activity.

EphB4 in Cancer Development

The function of the EphB4 receptor goes beyond only vascular development into cancer progression. Especially in its interactions with ephrinB2, EphB4 helps to control blood vessel development and preserves vascular integrity. However, the dysregulation of EphB4-ephrinB2 signaling is increasingly linked to several diseases, including mesothelioma, head and neck cancer, and lung cancer. Often increased in many cancer types, EphB4 fuels tumor angiogenesis—a feature of cancer progression.

EphB4 interaction with ephrinB2 enhances cell-cell contact and inhibits signaling pathways like the Ras/MAPK pathway that would otherwise drive tumor growth in normal cells. But in tumor cells, Eph receptors are commonly increased while ephrins are downregulated and the disturbance of cell-cell junctions reduces EphB4-ephrinB2 interactions. This mismatch results in increased signaling via other channels, including the crosstalk between EphB4 and other RTKs including ErbB2 and EGFR. The Ras-MAPK and RhoA GTPase pathways, which advance cell proliferation and tumor aggressiveness, are activated by this interaction.

Fascinatingly, the dual action of EphB4 in tumor development and repression reflects the intricacy of Eph/ephrin signaling. EphB4 may either stop tumor growth or help tumor advancement depending on the cellular setting. While this duality presents difficulties in focusing EphB4 as a therapeutic approach, it also emphasizes its potential to be selectively modulated to treat cancer.

Cancer Therapy Targeting EphB4

EphB4 has become a potential target for therapeutic intervention given its participation in cancer development, especially in upper aerodigestive tract tumors. Small chemical inhibitors as well as immunotherapeutic techniques have been investigated as means of reducing EphB4 activity.

Small Molecule Inhibitors Early studies have concentrated on creating tiny compounds either targeting blocking EphB4-ephrinB2 connections or kinase activity of the receptor. One such method is creating antagonistic peptides, such as TNYL-RAW, which bind strongly to EphB4 and hence disturb its interaction with ephrinB2. These compounds are under test for their capacity to stop tumor growth and prevent angiogenesis. Preclinical models are being used to assess the efficacy of these inhibitors; encouraging findings imply that EphB4 inhibition could be a successful approach for treating malignancies driven by abnormal EphB4 signaling.

Another intriguing strategy is immunotherapy aiming against EphB4. Investigating the creation of monoclonal antibodies and antibody-drug conjugates (ADCs) targeted especially against EphB4-expressing tumor cells researchers These treatments seek to guide the immune system to identify and destroy cancer cells expressing EphB4, therefore enhancing the results in malignancies that overexpress this receptor.

Another direction of study involves combining EphB4-targeting medications with other treatments such as chemotherapy, radiotherapy, or inhibitors of other RTKs. Combining treatments may have synergistic effects since EphB4 commonly interacts with other signaling pathways driving cancer growth, therefore enhancing the general therapeutic efficacy.

References:

  1. Salgia R, Kulkarni P, et al. EphB4: A promising target for upper aerodigestive malignancies. Biochim Biophys Acta Rev Cancer. 2018 Apr;1869(2):128-137.
  2. Chen Y, Zhang H, et al. Targeting receptor tyrosine kinase EphB4 in cancer therapy. Semin Cancer Biol. 2019 Jun;56:37-46.
  3. Noren NK, Pasquale EB. Paradoxes of the EphB4 receptor in cancer. Cancer Res. 2007 May 1;67(9):3994-7.
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